In the field of printing and bookbinding, devices and tools are known for processing the backs of blocks of sheet elements before applying an adhesive layer thereto for gluing a cover.
Generally, these devices and tools comprise a support that is adapted to rotate about a substantially vertical axis and to be coupled to a motorized spindle and an annular member that can be secured to the base and comprises a crown of milling blades formed on its outer edge.
During rotation of the support base, the blades mill the sheet elements of the block as it is being fed, at a cutting plane that is substantially perpendicular to the axis of rotation to flatten the sheets of the block and level the surface of the back.
A first type of tools is configured to only mill the sheets of the block. In an attempt to enhance the functions of the tool, tools have been developed which effect both milling of the sheet elements of the block and roughening of the block back, also known as notching or micro-notching.
By means of notching or micro-notching the back of the block is cut and roughed to increase the contact surface with the adhesive that is later applied to the block back before coupling with a cover.
In addition to milling blades, multifunctional tools also comprise a crown of roughening inserts that can be removably secured to the base along a circular area that is radially inwardly offset from the milling blades.
EP1378373 discloses a tool for milling and roughening the back of the block of sheet elements, which comprises a crown of roughening inserts projecting upwards from the cutting plane of the milling blades. The inserts have a prismatic body with a sharp upper edge adapted to interact with the back of the block as the base is rotated to cause cutting thereof. Furthermore, the tool comprises an additional annular member having a plurality of brushes for brushing the back of the block after the milling and notching operations.
A first drawback of this known solution is that the roughening inserts cause material removal, and damage the block portions contiguous to the back that shall not undergo this processing.
A further drawback is that the use of these inserts affords limited increase of the contact surface of the back for further application of the adhesive.
Another drawback is that the inserts interact with the block in a corresponding inclined direction, not adapted to create optimal cuts for notching.
A further drawback of this solution is that assembly and disassembly of the various parts of the tool are complex and labor-intensive operations.